SOFT ANATOMY AND THE AFFINITIES OF CONODONTS

Recent claims that conodonts are members of the Craniata or Vertebrata are based in part upon soft tissue features that have been preserved in a small number of specimens. These features include what appear to be radials in the caudal fin and paired structures that have been iden tified as eye remnants. The evidence for radials is limited, but credi ble. However, the anatomy of extant cyclostomes suggests that the pair ed structures are more reasonably interpreted as otic capsules than th e remnants of sclerotic eye capsules. Moreover, even if these structur es are the remnants of eyes, conodonts might equally well be a sister group to the craniates as a member of that group. Aside from these pai red structures, conodont fossils exhibit no features that are suggesti ve of a cartilaginous skeleton. Given that cyclostome fossils sometime s show evidence of the cartilages of the head, the apparent absence of a similar skeleton in conodont animals calls into question the claim that they are craniates. The simple single chevron shape of conodont m yomeres also suggests that they lie outside of the Craniata. All livin g craniates have double-chevron myomeres as adults, whereas simple myo meres of the conodont type are found in the non-craniate cephalochorda tes. Thus the available soft tissue evidence suggests that conodonts a re best regarded as the sister group of the craniates.